1. Field of the Invention
This invention relates to a video signal processing apparatus for processing a video signal produced from an image sensor, such as a solid-state image sensor, and, more particularly, to means for obtaining an accurate video signal by correcting the signal produced from the image sensor and for accomplishing contour correction with a simple arrangement.
2. Description of the Prior Art
In the television camera of the kind using a solid-state image sensor MOS, CCD, etc., the image sensor is composed of picture elements formed with cells which have a photo-electric effect and are two-dimensionally arranged on the surface of a monolithic semiconductor obtained by manufacturing technique for a highly integrated IC such as LSI, VLSI, etc. The solid-state image sensor produces, in a time serial manner, the photo-electric conversion outputs of these picture elements. A television signal is obtained from the output of the sensor.
For the TV camera of this kind, there have been proposed many image sensing methods (such as spatial picture element shifting method) and signal processing methods of correcting the output of the solid-state image sensor for the purpose of simplifying the structural arrangement of the solid-state image sensor. Further, in the case of a color TV camera, chrominance signals are taken out with a color separation filter arranged on the surface of the solid-state image sensor. Many methods also have been proposed for the arrangement of the image sensor and for processing the chrominance signal obtained in that instance.
Further, it has been practiced to obtain a contour signal by combining an original signal with a signal obtained by delaying the original signal for the purpose of correcting the contour of a video signal.
The solid-state image sensor performs a photoelectric converting operation on the quantity of light of the image of an object incident on the cells and analogically accumulates it. The cells somewhat differ from each other in the dark current produced from each of them due to unevenness in their output characteristics and imperfectness of crystals arising during the manufacture of them. This causes dark current irregularity. This irregularity must be minimized. If not, the output video signal would be affected thereby. This presents no problem for a device of the kind handing a digital signal as such a slight level error is erased during a binary coding process. However, as compared with an LSI or the like arranged to handle a digital signal, a solid-state image sensor handling a video signal must be arranged to minimize the unevenness of the outputs of cells and flaws of their crystals. Besides, there is a manufacturing difficulty in arranging many picture elements.
In order to improve the horizontal resolution and the vertical resolution among the basic performances of a TV camera, and to suppress a false signal from being generated, it is desirable to have picture elements arranged in a large number. This requirement then furthers the manufacturing difficulty.
Meanwhile, the vertical resolution can be doubled by performing an interlacing driving operation on the image sensor such as a solid-state image sensor. However, accurate interlacing is difficult due to inconsistency of the characteristics of solid-state image sensors and the use of a color separation filter.
Further, the conventional profile correcting arrangement necessitates use of one or a plurality of delay lines each of which is arranged to delay video signals for one horizontal line period. However, these delay lines are expensive because of their complex arrangement. The use of them, therefore, inevitably results in an increased cost of the whole apparatus.